A suspect in a plot to bomb the New York City subway system has pleaded guilty to terrorism charges.

In a New York court Friday, Zarein Ahmedzay admitted to conspiracy to use weapons of mass destruction and providing material support to al-Qaida. He faces up to life in prison.

Prosecutors say Ahmedzay, a U.S. citizen, plotted with Afghan-born Najibullah Zazi and another man to stage coordinated suicide attacks in the subway system last year, around the anniversary of the September 11, 2001 terrorist attacks.

The prosecutors say the suspects hoped to attack two of New York City's busiest stations - Times Square and Grand Central station.

Since his arrest in September, Zazi has provided authorities information about the plot. Officials say the attackers planned to position themselves in the middle of busy subway cars in order to kill the most people.

Zazi pleaded guilty to charges including conspiracy to use weapons of mass destruction. He is scheduled to be sentenced in June.

Prosecutors say Zazi spent more than a year plotting the attack with his co-conspirators. The U.S. government alleges he traveled to New York on September 10 to move forward with his plans. He was arrested in Colorado on September 19.

Law enforcement sources have said a fourth suspect has been arrested in Pakistan, although they have not provided further details.